Use a straight rolling pin (not a tapered pin) to work the dough to a thin oval or rectangle less than 1/8 inch thick. Every few seconds, lift the dough and dust under it with more flour and dust the top as needed to prevent the dough from sticking to the counter or the pin. If the dough resists and shrinks back, let it rest for a few minutes and move on to one of the remaining dough balls. Repeat the rolling process with each piece of dough.
Combine the egg with 1/2 cup water to make an egg wash. Brush the top of the dough with egg wash and lightly sprinkle with coarse sea salt. Cut the dough into desired size for crackers with a pizza cutter or knife or pastry blade (you also can use a small biscuit cutter).
Transfer the crackers to the pans, placing them very close together (they will not rise or spread). Place the pans in the oven (you can bake them all at once or 1 at a time). Rotate the pans after 8 minutes (if baking multiple pans, switch shelves). After another 8 minutes, rotate again.
